Impingement system in the drying section of a paper machine or the like

Abstract

The invention relates to an air impingement system arranged outside the jacket of an air impingement roll in the drying section of a paper machine or the like for heating and drying a web travelling around the said air impingement roll. The air impingement system comprises a mainly closed hood, which has control means for directing air onto the paper web. From the hood, air is directed by blowing with at least one fan to the blower nozzles and back again into the said hood as a circulation air process, and the system incorporates at least one heating device for heating the air. The air impingement system's hood and its said equipment are used in conjunction with an air impingement roll, which is of the size of approximately 1.5–2 m in diameter. The hood of the air impingement roll is at maximum 5 m high, preferably only 1.5–2.5 m high.

1. An air impingement system for heating and drying a web travelling around a roll of a drying section, comprising:
 a single hood positioned so as to surround a portion of the roll upon which the web travels in the drying section, the web wrapping around a lower portion the roll, the hood surrounding a portion of the web extending from proximate a location where the web separates from the roll on a trailing side of the roll and so that a portion of an incoming side of the roll where the web contacts the roll is not wrapped by the hood; 
 at least one fan; 
 a heating device for heating the air blown by the at least one fan; and 
 an air directing means for directing air blown by the at least one fan onto a portion of a surface of the web as the web travels around the roll within the hood; 
 wherein the hood is positioned so that air blown onto the web circulates within the hood. 
 
   
   
     2. The air impingement system of  claim 1 , wherein the hood surrounds the roll up to a maximum of 150°. 
   
   
     3. The air impingement system of  claim 1 , wherein at least some elements of the air impingement system are detachable. 
   
   
     4. The air impingement system of  claim 3 , further comprising at least one condensation device to aid in adjusting a moisture content of the circulating air. 
   
   
     5. The air impingement system of  claim 4 , wherein the heating device is located before the said at least one fan in the direction of air flow. 
   
   
     6. The air impingement system of  claim 1 , wherein the heating device comprises a gas burner having a length approximately the same as a width of the web. 
   
   
     7. The air impingement system of  claim 6 , further comprising a means for supplying combustion air to the gas burner at least partially from outside of the air impingement system. 
   
   
     8. The air impingement system  claim 1 , further comprising an air duct configured to direct air from the at least one fan to the portion of the surface of the web, said air duct being substantially straight. 
   
   
     9. The air impingement system of  claim 1 , comprising at least two fans. 
   
   
     10. The air impingement system of  claim 4 , wherein the at least one condensation device uses water as a cooling agent. 
   
   
     11. The air impingement system of  claim 1 , wherein part of the circulation air is directed out of and below the air impingement system. 
   
   
     12. The air impingement system of  claim 6 , further comprising a burner fan that brings air to the burner. 
   
   
     13. The air impingement system of  claim 9 , comprising three to five fans. 
   
   
     14. The air impingement system of  claim 12 , wherein the burner fan is located in the hood. 
   
   
     15. A method for heating and drying a web travelling around a roll of a drying section, comprising:
 positioning a single hood so as to surround a portion of the roll upon which the web travels in the drying section, the web wrapping around a lower portion the roll, the hood surrounding a portion of the web extending from proximate a location where the web separates from the roll on a trailing side of the roll and so that a portion of an incoming side of the roll where the web contacts the roll is not wrapped by the hood; and 
 directing heated air onto a portion of a surface of the web as the web travels around the roll within the hood. 
 
   
   
     16. The method of  claim 15 , wherein the hood surrounds the roll up to a maximum of 150°.